The present invention relates to a focusing controller for a collimating telescope used on a survey instrument.
Description will be given first on a conventional type focusing mechanism for a survey instrument referring to FIG. 3 and FIG. 4.
Even in the electronically designed survey instrument as recently developed, a collimating telescope is used for collimating a target object. The collimating telescope is provided with a controller that is required when an operator collimates the target object.
A leveling instrument 1 is mounted on a tripod 2, and a staff 3 is erected at a target point. In the leveling survey operation, the leveling instrument 1 is placed at a horizontal position. Then, graduation on the staff 3 is observed and read through a collimating telescope 5 of the leveling instrument 1, and difference in height is surveyed according to a graduation pattern 4 on the staff 3.
When the difference in height is surveyed by collimating the staff 3, it is necessary to perform focusing operation on the staff 3, and focusing accuracy of the collimating telescope 5 also exerts influence on the accuracy of the survey.
Now, a conventional type focusing unit 7 will be described referring to FIG. 4.
On the operator side of a body tube 10, an ocular lens 11 is mounted, and an objective lens 12 is mounted on the other side of the body tube 10. Inside the body tube 10, a sliding tube 13 is slidably arranged. A focusing lens (not shown) is mounted in the sliding tube 13, and a rack 14 extending in the direction of generatrix is formed on outer surface of the sliding tube 13.
A pinion shaft 15 is rotatably provided in a direction perpendicular to the axis of the body tube 10, and gear teeth are engraved on the tip of the pinion shaft 15, and this serves as a pinion gear 16 engaged with the rack 14. On an exposed end of the pinion shaft 15, a focusing knob 17 is fitted.
In the focusing operation, when a surveyor collimates the staff 3 through the objective lens 11, the focusing knob 17 is turned. Then, the pinion shaft 15 is rotated, and the sliding tube 13 is moved along the optical axis via the rack 14, and optimal focusing condition is attained.
In the conventional type leveling instrument as described above, a graduation pattern 4 on the staff 3 is read. Whether the reading of values is accurate or not depends upon the skill of the surveyor. Variations between the surveyors are eliminated by taking average of the read values. With the introduction of numerical value processing, difference of the measurement accuracy between beginners and skillful operators is now not very conspicuous. However, since the focusing mechanism is still operated manually as described above, there are considerable differences in operational time and skill between beginners and experienced operators. In case the operator is not very familiar with focusing operation, the leveling instrument may be inadvertently vibrated or jerked, thus impairing leveling condition of the leveling instrument. Further, the impairment of the leveling condition may directly exert influence on the measurement accuracy.